Process for improving the odor of cellulosic pulp by-products



United rates RDCESS FOR IMPROVING THE ODOR OF CELLULOSIC PULP BYJRODUCTS Walter Christian Mcnly, New Brunswick, N. 3., and

Breckenridge K. Tremaine, Wilmington, DeL, assignors, by mesne assignments, to Rhodia, 11%., New York, N. Y., a corporation of New York No Drawing. Application March 4, 1953, Serial No. 340,408

materials of the cellulosic material which consist essentially of lignin are dissolved, leaving the pulp as a fibrous residue dispersed in a black liquor which contains sodium hydroxide and sodium sulfide. The pressure in the digester builds up due to the formation of steam and noncondensed gases which must be relieved from time to time. These gases contain small amounts of hydrogen sulfide, dimethyl sulfide, methyl mercaptan, and traces of ethyl. and amyl mercaptans which form by the interaction of lignin and sodium sulfide and have a very persistent clinging malodor which renders the atmosphere extremely unpleasant in the neighborhood of the mill, and may be detected for miles around.

These odorous by-products are the cause of the malodor, because they are released at various stages and in various places during the pulping and recovery operation. Some odor is released with the relief gases, more with the blowdown and further amounts at the evaporators and cascades and several minor locations. This release at different locations makes the removal by scrubhing and similar physical or chemical methods expensive. On theother hand, spraying of odorants at various places in the pulping mills is ineffectual, because apparently. the areas are so great that malodor and odorant do not mix sufficiently.

When the cooking operation in the digester has been completed, the charge is blown out and the pulp is separated from the black liquor. This is technically called the blowdown. The black liquor is separated from the pulp and concentrated to a black syrupy liquid containing large amounts of lignin derivatives which is then sprayed as a fuel into a furnace to recover heat and chemicals.

This invention is concerned with the elimination of the offensive odor imparted to the atmosphere mostly when the digester is relieved during cooking, and at the digester blowdown. Heretofore, many expedients have been resorted to in attempts to remove the sulfur compounds which are responsible for the obnoxious odors released into the atmosphere. Some of these methods involve means such as scrubbing, absorption, oxidation with chlorine, burning etc., but all of them require expensive and cumbersome equipment.

This problem is very serious in the paper industry, and in Pulp and Paper Mag, Canada, 24, 1381 (1926), E. Hagglund made the statement that The growth of the sulfate pulp industry has been retarded materially owing to the inability of the manufacturer to eliminate or reatent duce the presence of undesirable odors in the mill and its surroundings." As a result, uneconomical locations are necessarily selected for the paper mills. It will be apparent, therefore, that if a method could be devised to eliminate the odors or render them unobnoxious, an extremely important economic problem in the paper industry would have been solved.

It is therefore an object of the present invention to provide a simple process for practically eliminating the malodors arising from the paper mills of the type described above. Another object is the provision of a simple method which reduces malodors with a minimum of expense and interference with the normal function of the paper mill. Other objects will appear as the desciption of the invention proceeds.

These and other objects are accomplished by introducing into the digester a small amount, usually from 1 to p. p. in. (parts per million), and preferably from 5 to 100 p. p. m., of a reodorizing agent consisting essentially of a mixture of odorous organic compounds based on the total weight of the digester content more fully described hereinafter.

The chemical constitution of the reodorizing organic materials added to the digester is not particularly critical except that their odors must not be destroyed in the digester. It has been found that any organic compound which retains its odor after being heated for one hour at C. with a solution of 4% NaOH and 2% NazS in water is satisfactory. It will be found, however, that most esters, lactones, acids and phenols undergo'a chemical change which destroys their odor during this treatment with alkali so that such compounds are unsatisfactory. In general certain members in the categories of hydrocarbons, alcohols, ethers, aldehydes, ketones, amines and heterocyclic compounds having a strong odor are satisfactory.

The reodorizing compounds to be added to the digester should have a high odor quantity which may be determined as disclosed in U. S. Patent No. 2,136,844. A great deal of research has been done to determine the amount of odor possessed by various compounds, and for the purpose of the present invention the simplest method of determining the operability of any organic compound may be found by observing the minimum detectable concentration of the compound under observation in water or air. This concentration is called the odor threshold value, and is expressed as the concentration of odorant in parts per part of water or air. The following values taken from the literature are illustrative:

Odor threshold concentration in air in parts per million Odorant Methanol 800 Chlorophenol .603

F 10 p. p; m. to be of value in the present invention, and

preferably less than 1 p. p. m.

The following compounds arranged by classes are illustrative of those which are operative and produce very satisfactory results. In the preferred embodiment of the invention, organic material containing at least one compound from each of the three classes should be added to the digester, although some of the compounds yield improvement alone or in combination with one other compound.

Class I Low boiling odorants (boiling point below 200 C.)

Butyric aldehyde Valerie aldehyde Octylaldehyde Choline Butylamine Pyridine and alkylpyridines Nitrobenzene Octanol-l Octanol-2 Benzaldehyde Class II Medium boiling odorants (boiling point 200-250 C.):

Camphor Borneol Isoborneol Acetophenone Phenylethyl alcohol Citronellal Geraniol Laurie alcohol Citronella oil Cedarwood oil Pine oil Terpineol Class III High boiling odorants (boiling point above 250 C.): Ionones Ionone terpenes Skatole Indole 2,3-dimethyl indole Alpha-naphthylamine 'Alpha-naphtho1 methyl ether Beta-naphthol methyl ether Beta-naphthol ethyl ether Benzophenone Methyl naphthyl ketone Diphenyloxide Diphenyl Diphenyl methane Benzal acetone Benzyl trimethyl ammonium hydroxide As mentioned above, a single organic material of the type described shows some improvement, but best results have been observed when a mixture of at least 5 to organic compounds are used with preferably at least two being selected from each of the above-mentioned boiling point classes.

The following examples are given by way of illustration, although it is to be understood that the proportions of the ingredients and their substitution by one or more compounds selected from the above Table I may be varied, provided a plurality of reodorizing agents are used, each of which has a boiling point between 50 and 400 C., and preferably at least one compound of the mixture has a boiling point falling within each of the above classes and is present in the amount of at least 1% of the mixture of organic compounds.

Example I A typical sulfate process digester, which is indirectly heated, is charged with 55,000 pounds pine Wood chips (containing 30,000 pounds moisture-free wood) and with 60,000 pounds of white liquor, consisting essentially of a water solution of 4,000 pounds caustic soda and 2,000 pounds of sodium sulfide. In addition there is added 35,000 pounds of dilute black liquor recovered from a previous digester operation. The total charge is 150,000 pounds. To this charge is added manually or by means of proportioning equipment 3.0 pounds of a reodorizing agent of a composition comprising one-half pound each of n-butyraldehyde, pyridine, geraniol, isoborneol, ionone and benzophenone. The concentration of reodorizing agent is thus 20 p. p. m. calculated on the contents of the digester. The digester is now closed tightly and heated at 150 to 180 C. for 2 to 6 hours. At the end of the heating period the bottom valve is opened and the contents of the digester are blown by the internal pressure into a blow tank, while the steam and vapors are released into the air or partially condensed in a condenser system. The suspension of delignified cellulose wood fibers in the blow tank is separated by filtration into wood pulp and black liquor. The wood pulp is further washed free from black liquor with water and may amount to 12,00015,000 pounds on a dry basis. Black liquor and wash waters are concentrated in an evaporator system until the solids content of the mass reaches about 60% to After the mill had been in operation for some time, it is noted that the malodors usually present had been abated. The nauseating sweetness of the mercaptans had been reodorized and the area within the mill and for several miles outside the mill is distinctly improved. This improvement is particularly noticed during the digester relief, blow-down steam, condensate and non-condensed gases, black liquor, pulp washers, condensate and vapors from evaporators, and stack gases after passing through the contact black liquor evaporators and, depending on atmospheric conditions, for several miles downwind from the mill.

Example 11 The above example is repeated, but in place of the reodorizing agents of Example I, one pound of a mixture containing equal parts of butylamine, laurie alcohol, and diphenyl oxide are added to the digester.

Example III Satisfactory results are also found when Example I is repeated using 15 pounds of equal parts of n-butylamine, pyridine, dipentene, isoborneol, geraniol, n-butyraldehyde, benzophenone and ionone. While the reodorizing agents in this example represent about parts per million based on the charge of the digester and produce satis factory results, such high concentration is usually not necessary.

While the invention has been illustrated by the use of pine chips in the pulping operation, it is to be understood that straw, flax, bagasse and wood from various trees may be substituted in the examples for the pine chips.

It has been observed that when the mill is operated without the addition of the reodorizing agents, the atmosphere is contaminated with sulfides and mercaptans. The concentration in the air is extremely small but, nevertheless, is sufiicient to be a very obnoxious nuisance. These odors have the peculiar property of clinging persistently to fabrics, such as clothing, automobile upholstering, furniture and the like, probably due to absorption within the cellulose or other fibers. The odor can be detected on clothing or in automobiles for hours after their removal from the foul atmosphere. When the mill has been in operation according to Example I of the present invention for some time, neither the odor of the mercaptans nor reodorizing agents can be detected on clothing or in automobiles located in proximity to the mill. When the same reodorizing chemicals are sprayed into the atmosphere, no significant reodorizing is observed and usually both the malodors and reodorizing agent can be smelled separately.

It has also been found that, while the greatest improvement due to the use of the invention is found in the relief gases, digester blow-down, and the atmosphere for several miles outside the mill, great improvement is also noticed in the rotary washers for washing the pulp after discharge from the digester, and in the condensate from the evaporation of the heavy black liquor.

The primary advantage of the invention lies in the fact that as little as 2 to 8 ounces of reodorizing agent per ton of paper pulp produced is necessary to eliminate the malodors originating from the mill. Another advantage of the present invention is that the cost of eliminating or reducing the odors is practically negligible, and does not interfere in any way with the normal operation of the digester or other equipment in the mill and the quality of the pulp.

These advantages are accomplished largely because the reodorizing agent is selected to have a degree of volatilization into the atmosphere which parallels the release into the air of the malodorants. The pulping process is very complex and it is surprising that the applicants expedient is successful in coordinating the release of reodorizing agent and malodorant so effectively at the several stages of the pulping process.

It will be apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

We claim:

In the sulfate digestion process of pulping ligno-cellulosic material wherein the said material is digested with the resulting formation of malodorous compounds, the improvement which comprises introducing into the digester from 1 to parts per million, based on the digester charge, of a mixture of at least three odor-bearing organic compounds, at least one of said organic compounds being selected from the class consisting of, butyric aldehyde, valeric aldehyde, octylaldehyde, choline, butylamine, pyridine and alkylpyridines, nitrobenzene, octanol-l, octanol-Z, benzaldehyde, at least another of said organic compounds being selected from the class consisting of, camphor, borneol, isoborneol, acetophenone, phenylethyl alcohol, citronellal, geraniol, lauric alcohol, citronella oil, cedarwood oil, pine oil, terpineol, and at least one other of the said organic compounds being selected from the class consisting of, ionones, ionone terpenes, skatole, indole, 2,3-dimethyl indole, alpha-naphthylamine, alpha-naphthol methyl ether, betanaphthol ethyl ether, benzophenone, methyl naphthyl ketone, diphenyloxide, diphenyl, diphenyl methane, benzal acetone, benzyl trimethyl ammonium hydroxide.

References Cited in the file of this patent Casey, Pulp and Paper, vol. I, pp. 141, 143.

Crocker, Chemical Industries, June 1949, pp. 948, 950, 952.

Paper Trade 1., June 29, 1911, p. 54. 

